Plate Nº 33 · recorded October 10, 2026
PhysicsReported finding
DarkSide-50 narrows the search for nuclear dark matter
After a seven-year search in an underground liquid-argon detector in Italy, the DarkSide collaboration found no signal for composite 'nuclear' dark matter — but ruled out many ultraheavy candidates, paving the way for DarkSide-20k in 2027.
By Marcus Bennett3 min read641 words
In brief
- The DarkSide collaboration completed a seven-year experiment using the DarkSide-50 detector at Italy's Laboratori Nazionali del Gran Sasso.
- Data was collected between 2013 and 2020, with results published September 28, 2026 in Physical Review D.
- The search found no direct evidence of composite 'nuclear' dark matter, but ruled out a wide range of candidate properties.
- Dark matter accounts for roughly 85% of the universe's mass.
- DarkSide-20k, planned for 2027, will use roughly 1,000 times more liquid argon than DarkSide-50.
A seven-year experiment at the world's largest underground research facility has ruled out a wide swath of composite "nuclear" dark matter candidates, the DarkSide collaboration reported on September 28, 2026 in Physical Review D.
The analysis draws on data collected between 2013 and 2020 by the DarkSide-50 detector, which sits inside a mountain at Italy's Laboratori Nazionali del Gran Sasso. The collaboration searched for an unconventional form of dark matter: particles that behave less like single points and more like atomic nuclei, with their own internal structure.
What is "nuclear" dark matter?
For decades, the leading explanations for dark matter have assumed it consists of elementary particles — indivisible points that cannot be broken down further. The two most-studied candidates are axions and weakly interacting massive particles, or WIMPs. Both pass through ordinary matter largely unnoticed, betraying themselves only through gravity.
Yet as direct detection efforts have repeatedly come up empty, physicists including Jocelyn Monroe at the University of Oxford have explored a different possibility. "About a decade ago, my collaborators and I explored the possibility that dark matter might instead have its own nuclear physics," Monroe said.
Under this picture, "dark particles bind together in the early universe to form very large 'dark nuclei,' potentially containing billions or vastly more constituents." The idea reframes dark matter as something closer to a microscopic version of ordinary matter: bound states of smaller "dark nucleons," rather than solitary points.
How does DarkSide-50 detect these particles?
DarkSide-50 centers on a cylindrical tank of liquid argon buried deep beneath the Gran Sasso mountain. The rock overhead shields the detector from cosmic rays that would otherwise drown out the faint signals physicists hunt for.
The experiment watches for tiny flashes of light that should appear when a dark matter particle strikes an argon nucleus and knocks it aside, depositing energy in the liquid. A simple WIMP would produce one such recoil as it crosses the detector. A composite particle, because of its larger size, could leave multiple.
"The key distinction is that the analysis takes their internal structure into account," Monroe explained. "The dark matter has a finite size and a corresponding form factor — a quantity describing how a particle's scattering strength depends on its size — and a single object can potentially scatter several times as it passes through the detector."
The collaboration developed new analysis methods to look specifically for these multi-recoil patterns, applying them across the entire seven-year dataset.
What did the search find?
The team found no evidence that composite dark matter interacts with argon nuclei in the predicted way. Still, the absence of a signal carries weight: it lets researchers eliminate a broad range of possible masses, sizes, and binding structures for ultraheavy nuclear dark matter.
In effect, the experiment narrowed the hunting ground for future searches. "An interesting feature of the result is that the sensitivity depends on the properties of the constituents — the 'dark nucleons' — showing that the internal structure of the dark matter can have observable consequences," Monroe added.
What's next for the DarkSide program?
Dark matter makes up roughly 85% of the universe's mass, according to cosmological measurements, yet scientists still do not know what it is. Identifying its true nature would reshape fundamental physics.
The DarkSide collaboration plans to install DarkSide-20k in 2027. The new detector will hold roughly 1,000 times more liquid argon than its predecessor and should sharpen the search by orders of magnitude.
"This will open up the long-term possibility of potentially observing 'dark chemistry' signatures," Monroe predicted. "More immediately, this work shows that existing experiments can test dark matter candidates that look very different from the conventional WIMP."
The full results appear in Physical Review D under the DOI 10.1103/r3zg-zlfg, authored by P. Agnes and collaborators.
via Phys.org Physics (Source)
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